Electric Airplanes, contra-rotating propellers

[wumpus]

3 minutes ago, micha said:

If that relies on superconductors as shown in the last video of the OP, we have a while to wait yet. Yes, the superconductor cables themselves are only grams compared to KG's for copper, but even "warm" superconductors are still running at -250C or thereabouts (there are warmer examples, but rather esoteric and not really practical in an engineering solution), so you need heavy and power-hungry cooling equipment.

Room-temperature superconductors (ie, > 0C, not even 20C!!) are the holy grail, whoever invents or discovers a usable one will change the world.

Except that passenger jets have access to arbitrary amounts of -35C (more typically -50C, but you can only count on -35C) air.  Don't forget that "warm" levels is cheaply available (by using liquid nitrogen as a coolant), and superconducting equipment shouldn't be generating heat that uses up that coolant.

I suspect that regulations on how far a plane needs to coast after losing "x amount" of engines will take some engineering (if this means that the plane will fly lower with less motors) as well as issues as to just what happens when the coolant fails and the electricity is shoved into the copper "insulation".  But don't assume that planes need anywhere near "room temperature" (and remember that cars are expected to drive from Phoenix to Palm Springs in the summer, so moving from the industry that is likely driving development to planes should be pretty easy).

[DDE]

19 hours ago, magnemoe said:

batteries has to do without

Point of order!

They are the supposed silver bullet that gets batteries into chemical fuel territory in terms of energy density.

[DerekL1963]

3 hours ago, wumpus said:

Except that passenger jets have access to arbitrary amounts of -35C (more typically -50C, but you can only count on -35C) air.

Once they're at cruising altitude, yes.   Down lower, not so much.

And don't forget the drag added by the intakes needed to access that cold air.

[magnemoe]

3 hours ago, DDE said:

Point of order!

They are the supposed silver bullet that gets batteries into chemical fuel territory in terms of energy density.

I know, just zinc / air would be an major game changer. An bonus would be safety as you can stop an fire just by stopping air intake, optionally flush with inert gas like co2. 

[wumpus]

18 hours ago, DerekL1963 said:

And don't forget the drag added by the intakes needed to access that cold air.

Only after I've tried a few ways to use the wing surfaces as heat sinks.  That's a lot of surface area with a lot of air moving across it.  I might even get lift if I just use the lower surfaces.

No idea how often ground personnel touch the wings, but at least it is a controlled environment.

[peadar1987]

On 27/10/2017 at 4:53 PM, mikegarrison said:

Few aspects of airplane design end up being "trivial". Such a design would severely constrain where the batteries could be located, because they would have to able to accessed from outside the airplane and most likely slid in and out using heavy equipment. In all sorts of weather. Within the gate box space constraints for service vehicles. They would have to be 100% reliably secure when you installed them, and yet reasonable easy to detach and reattach. I think this would be a bigger chore than you anticipate.

Oh I know it wouldn't be "trivial trivial", probably not the best choice of words. Just that it would be far less of an engineering and technological challenge than actually getting appropriate batteries. 

On 27/10/2017 at 4:51 PM, DerekL1963 said:

Things are always simple seen from the armchair.   The labor costs alone make this a nonstarter.

I don't see any reason why this would have any higher labour costs than using liquid fuel. 

[Steel]

6 hours ago, peadar1987 said:

I don't see any reason why this would have any higher labour costs than using liquid fuel. 

With fuel you essentially just connect a pipe into the fuel system/truck and pump it into the plane. With a battery pack you have to transport them to and from where they're being charged (baring in mind they will probably mass about 50% of the total plane mass), ensure that they are being charged properly, inspect them for damage and deterioration e.t.c. That's before you get to the logistical headache of making sure you have charged batteries ready to go and in the correct place when required.

Edited October 29, 2017 by Steel

[wumpus]

3 hours ago, Steel said:

With fuel you essentially just connect a pipe into the fuel system/truck and pump it into the plane. With a battery pack you have to transport them to and from where they're being charged (baring in mind they will probably mass about 50% of the total plane mass), ensure that they are being charged properly, inspect them for damage and deterioration e.t.c. That's before you get to the logistical headache of making sure you have charged batteries ready to go and in the correct place when required.

Except that current planes have to be fueled with fuel and loaded with cargo that has all of these issues plus COM issues (mostly for the cargo).  While I strongly doubt that battery packs will be swapped (compare electric cars vs. fueled cars and planes vs. fueled cars/passenger vs. planes.  I'd expect each passenger will require a Tesla-sized battery), most of these issues seem overdone.  I'd also expect that inspection can be automatic, as any damage will show up as power/capacity loss during charge/discharge cycles.

It really comes down to which the airlines hate more: fuel consumption or mass.  Right now the mass can't justify fuel consumption (and remember those turbines are much more efficient than anything in a car, it will take a lot longer to cut airline fuel consumption than just switching to electric).

[YNM]

28 minutes ago, wumpus said:

While I strongly doubt that battery packs will be swapped

This one crops out earlier in the thread. Basically having to do with charging rates and airplane "downtime". It can also because the batteries aren't exactly rechargeable, like I've heard some arguments for the depleted batteries to just be recycled somewhere else (essentially recharging).

28 minutes ago, wumpus said:

I'd also expect that inspection can be automatic, as any damage will show up as power/capacity loss during charge/discharge cycles.

Batteries are extremely finicky. Once they conk out the conk out in a snap. At least that's the case with dry lead batteries found in cars and motorcycles, sort of the case with alkaline batteries, not so much for non-alkaline AA or such batteries, but I suspect lithium batteries will do the same - it could even be explosive.

Edited October 29, 2017 by YNM

[DerekL1963]

1 hour ago, wumpus said:

I'd also expect that inspection can be automatic, as any damage will show up as power/capacity loss during charge/discharge cycles.

Ah - so damage to the mechanical connections holding the battery in the aircraft will show up as power/capacity loss?  As will physical damage to the case?  No, they won't.  There's a lot more to maintaining and managing swappable batteries than managing and maintaining disposable (dry cell or rechargeables) or fixed installation (everything from your phone to the Model 3) batteries.  There's  a lot more to it than just examining the power and capacity curves. 

And that's where a good chunk of the increased labor costs come from.  Plus managing the inventory.  Plus operating and maintaining all the relevant handling and recharging equipment.

[mikegarrison]

With fuel, you very nearly have 100% power capacity right up until you run out of fuel, then you have none.

There is no battery that I am aware of that works like this. Typically the amount of power available falls off in a curve that is similar to (but not the same as) the amount of energy available. Most batteries still have energy available in them when they stop being useful, but the available power (voltage) has dropped enough that the device the battery is powering can't make use of it anymore.

[YNM]

30 minutes ago, mikegarrison said:

With fuel, you very nearly have 100% power capacity right up until you run out of fuel, then you have none.

There is no battery that I am aware of that works like this. ...

Alkaline and dry/low maintenance lead batteries ?

[mikegarrison]

45 minutes ago, YNM said:

Alkaline and dry/low maintenance lead batteries ?

Voltage falls off the entire time. Compare to jet fuel, which has the same BTU/kg from the start of the tank to the last drop.

[magnemoe]

2 hours ago, YNM said:

This one crops out earlier in the thread. Basically having to do with charging rates and airplane "downtime". It can also because the batteries aren't exactly rechargeable, like I've heard some arguments for the depleted batteries to just be recycled somewhere else (essentially recharging).

Batteries are extremely finicky. Once they conk out the conk out in a snap. At least that's the case with dry lead batteries found in cars and motorcycles, sort of the case with alkaline batteries, not so much for non-alkaline AA or such batteries, but I suspect lithium batteries will do the same - it could even be explosive.

Planes tend to have special maintenance anyway, reloading ordinance on warplanes is also well drilled, 
You could make an quick charger for an plane, problem is that this will be an even more specialized structure at gate. 
Replaceable battery packs has the benefit in that you can dump them. 

Electrical planes has two major benefit, they are quite and you can make them to use short runways, adding extra engines for fast takeoff is pretty simple.
An small feeder plane going from an downtown airport to the international is probably the main target for an electrical plane. 

[mikegarrison]

2 hours ago, magnemoe said:

An small feeder plane going from an downtown airport to the international is probably the main target for an electrical plane. 

People are studying electric planes (and hybrid planes) for other applications too, but I agree they are likely to be first successful as personal light planes and small air taxis.

[mrfox]

https://batterybro.com/blogs/18650-wholesale-battery-reviews/98659398-electric-jumbo-jets-how-many-batteries-do-you-need-to-get-airborne

 

 

[MatterBeam]

Flywheels using Zylon can reliably offer 1000Wh/kg:

http://www.tankonyvtar.hu/hu/tartalom/tamop425/0048_VIVEM319EN/ch08.html

[DerekL1963]

1 hour ago, MatterBeam said:

Flywheels using Zylon can reliably offer 1000Wh/kg:

http://www.tankonyvtar.hu/hu/tartalom/tamop425/0048_VIVEM319EN/ch08.html

Did you actually read that before linking?  Here is the relevant part (emphasis added) "Table 8‑1 Theoretical maximum energy density of some possible flywheel materials", and "These values could be achieved if the shape factor and all alpha factors would be unity. This is unfortunately not possible, at system level the achievable energy density is between 2‑12 % of the above theoretical one".

Or, in other words - not only does your source fail to support your claim that Zylon wheels can "reliably" do do...  It plainly states that the achievable energy is actually a fraction of what you claim.

[Northstar1989]

On 10/26/2017 at 4:20 PM, YNM said:

I thought that moveable CG would be better !

--------

 

Thrust generation comes best when the exhaust comes close to the airspeed. It's just a fun thought seeing future "jets" aircraft basically being a lifting gas - less airships !

A Center of Gravity that moves during flight as fuel is consumed has the potential to destabilize an aircraft (if the Center of Mass of the fuel is fore of the CoM of the aircraft as a whole).  It also necessarily limits design-choices.  A CoM that stays fixed in place liberates the designer...

As for the 2nd bit- you hit the nail on the head.  Thrust generation for an airbreathing vessel is maximized when exhaust velocity matches airspeed.  Which is why jets produce more thrust than propellers at high speeds, but less at low speeds...  (jets have a higher exhaust velocity than propellers)  Since people want to get to their destination FAST, and higher flight speeds allow higher (and therefore less turbulent) cruising altitudes, it's likely any *successful* electric aircraft will use electric turbofans for their higher exhaust velocities...

[Northstar1989]

On 10/27/2017 at 11:51 AM, DerekL1963 said:

Things are always simple seen from the armchair.   The labor costs alone make this a nonstarter.

Oh the irony!  (to say people know nothing from the armchair- then make such an inaccurate claim...)

The labor costs would be *trivial* compared to all the other labor costs already incurred in operating an airline industry.  More than made up for by the fuel-savings costs.  It's not that it would be cheap.  It's that all the other costs of running an airline- including fuel- are absolutely massive.

On 10/27/2017 at 11:53 AM, mikegarrison said:

Few aspects of airplane design end up being "trivial". Such a design would severely constrain where the batteries could be located, because they would have to able to accessed from outside the airplane and most likely slid in and out using heavy equipment. In all sorts of weather. Within the gate box space constraints for service vehicles. They would have to be 100% reliably secure when you installed them, and yet reasonable easy to detach and reattach. I think this would be a bigger chore than you anticipate.

A chore, yes.  Difficult, ABSOLUTELY.  But far from impossible.  Far greater hurdles are overcome in aerospace design on a daily basis.

Most likely you'd slot the batteries in the bottom of the fuselage, similar to where checked luggage is currently stored.  This would also allow you to make the wings thinner (reducing their drag), since fuel wouldn't be stored in them anymore...  So you'd trade off thinner wings for a longer fuselage, with the extra internal volume dedicated to batteries rather than passengers...

The fuel-savings are also *MUCH* more substantial than you think.  Consider that on a Sydney to Los Angeles A380 flight, fuel-costs amount for $244,539 of the $305,735 cost of a 484-passenger flight.

http://www.opshots.net/2015/04/aircraft-operating-series-aircraft-operating-expenses/

So, if batteries costed 1/3rd what jet fuel costs to power such a flight (amortizing out the cost of purchasing the batteries over all the flights they'll be used on in an average service life), you could comfortably cut the passenger-capacity in HALF to make room for all the batteries, and still have a lower cost-per-passenger than the traditional 484-seat A380 flight...

And, of course, it's easier to fill out all the seats on a 242-seat aircraft than a 484-seat one.  You could probably eventually (once the technology is established) even charge passengers *slightly* more for the electric flight, as it would be quieter...  And you could DEFINITELY make an argument for tax-incentives from the government as you aren't creating as much air pollution...

Edited January 25, 2018 by Northstar1989

[mikegarrison]

45 minutes ago, Northstar1989 said:

Thrust generation for an airbreathing vessel is maximized when exhaust velocity matches airspeed.

No. Propulsive efficiency is related to 1/(1-Ve/V0), so it gets highest as Ve=V0. But thrust is related to Ve-V0, so thrust goes *down* as exhaust velocity gets closer to the free stream.

Basically, as Ve approaches V0 the propulsive efficiency goes to infinity and the thrust goes to nothing. Since the thrust is nothing, it doesn't matter that the propulsive efficiency is at its peak -- the engine is still useless.

[Northstar1989]

3 minutes ago, mikegarrison said:

No. Propulsive efficiency is related to 1/(1-Ve/V0), so it gets highest as Ve=V0. But thrust is related to Ve-V0, so thrust goes *down* as exhaust velocity gets closer to the free stream.

Basically, as Ve approaches V0 the propulsive efficiency goes to infinity and the thrust goes to nothing. Since the thrust is nothing, it doesn't matter that the propulsive efficiency is at its peak -- the engine is still useless.

You're mis-applying formulae.  Thrust per kg of air goes down, but due to the higher propulsive efficiency and lower exhaust velocity you can accelerate a lot more air with the same energy.  Thrust, after accounting for these factors and properly increasing airflow, increases when exhaust velocity approaches airspeed.

[mikegarrison]

52 minutes ago, Northstar1989 said:

This would also allow you to make the wings thinner (reducing their drag), since fuel wouldn't be stored in them anymore...  So you'd trade off thinner wings for a longer fuselage, with the extra internal volume dedicated to batteries rather than passengers...

Making thinner wings would not be terribly useful for an airliner. Modern airfoil design prefers a relatively thick wing for transonic flight anyway. Supersonic is different -- the thinner the better.

Also, if you take the weight of the fuel out of the wing and put it into batteries in the fuselage it would very structurally inefficient due to the effect it would have on the wing root bending moment. It's much better to have the weight distributed out on the wing. The first place they would want to stuff batteries would be the wing.

2 minutes ago, Northstar1989 said:

You're mis-applying formulae.  Thrust per kg of air goes down, but due to the higher propulsive efficiency and lower exhaust velocity you can accelerate a lot more air with the same energy.  Thrust, after accounting for these factors and properly increasing airflow, increases when exhaust velocity approaches airspeed.

No I'm not. Just think about it using Newton. If Ve=V0, where do you get any thrust from? Statically that would mean there is no air coming from the engine at all.

Edited January 25, 2018 by mikegarrison

[Northstar1989]

12 minutes ago, mikegarrison said:

No I'm not. Just think about it using Newton. If Ve=V0, where do you get any thrust from? Statically that would mean there is no air coming from the engine at all.

This is a limit problem.  The closer you get to Ve=V0 the more air is required for maximum thrust.  You reach a point where it takes more air than there is mass in the universe to reach maximum thrust long before you reach Ve=V0, and obviously you can't examine the two when they're actually equal.

But, within practical limits, the closer your exhaust velocity is to your airspeed the more Thrust you can generate within the frame of reference of that V0.  E= 1/2 mv^2 but Thrust = mv.  The less kinetic energy you give each molecule of exhaust the more momentum you can generate by spreading your energy over more molecules...

Again, all of this within practical limits.  You don't want an air intake larger than your plane! (And the Drag produced would be enormous!)

Edited January 25, 2018 by Northstar1989

[mikegarrison]

It's not a "limits problem" per se.

First: you were simply wrong when you said that Ve=V0 maximizes thrust. That actually produces zero thrust. Thrust is maximized by "moar boosters" -- just get yourself bigger and more powerful engines if you need more thrust.

Second: Propulsive efficiency isn't everything. Thermal efficiency is the other half of engine efficiency, and then you have to consider weight, cost, engine size, noise, desired cruise speed, etc., etc. It is true that when you put everything together, a good propeller engine has an advantage at low speed over a good jet engine, and a good jet engine has an advantage over a good propeller engine at high speeds. Turbofans exist because they are kind of a hybrid of the two and work pretty well to bridge the gap over all the operating range of a high-subsonic cruise speed airplane.